The rate of synthesis of the individual ribosomal proteins of the large and small ribosomal subunits will be studied in cultured human cells, in order to determine if synthesis of these proteins is the limiting factor governing ribosome synthesis. The isolation of mRNA coding for ribosomal proteins will be attempted, with the intent of studying the flow of such RNA to the cytoplasm of human cells under varying growth conditions. An attempt will also be made to isolate and characterize a repressor of initiation of translation of mRNA for ribosomal and other proteins in human cells.